1. Field of the Invention
This invention relates generally to a still color television signal recording and reproducing apparatus, and more particularly to such an apparatus which utilizes a single storage tube of a conventional type.
2. Description of the Prior Art
It is well known in the prior art that a certain selected field or frame of a monochrome television signal is stored on a target of a storage tube utilizing electron beams modulated by the television signal and the stored signal is read out afterwards for a still television signal reproduction by scanning the target of the storage tube repeatedly with non-modulated electron beams.
Such an operation of a conventional storage tube is described, for example, in papers published in the IEEE Transactions on Electron Devices, vol. ED-18, No. 4, April, 1971, "Electronic Image Storage Utilizing a Silicon Dioxide Target," by R. S. Silver and E. Luedicke, pp 229-235.
The biasing voltage for the target electrode of the storage tube upon a WRITE mode is made different from that upon a READ mode such as described in the papers mentioned above and, for example, the target voltage of +200 volts upon the WRITE mode is decreased to +8 volts upon the READ mode. Therefore, the velocity of the electron beams between the G4 and the target electrodes becomes slower for the READ mode than that for the WRITE mode, so that the raster size on the target for the READ mode becomes larger than that for the WRITE mode. And further the raster shape on the target for the READ mode becomes twisted as compared with that for the WRITE mode as shown in FIG. 1A, because the scanning electron beams are differently rotated by a focusing magnetic field of the storage tube.
Now thinking of storing and reading a color television signal in and from such a single storage tube, a first serious trouble arises that the frequencys of a color signal component and a color burst component included in the color television signal read out from the storage tube become different from the original frequencys previously stored in the storage tube. And further a second serious trouble arises that the phases of the color signal component and the color burst component read out from the storage tube become shifted every horizontal period, because the raster shape for the READ mode is twisted and the electron beams are directed along the dotted lines shown in FIG. 1B at the beginning of every horizontal scanning period where waveforms shown in FIG. 1B represents electron charge pattern of every horizontal period on the target of the storage tube.
Such a phase shift accumulatively causes a frequency deviation after a number of horizontal scanning periods. In the prior art no simple or practical way was found to solve the first and the second serious troubles mentioned above.